Application of Seismic Methods in Larderello – Travale Geothermal Fields

Tuscany, Italy

Presented by : Presented by : Yulini ArediningsihYulini Arediningsih

April 14, 2009April 14, 2009

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OutlineOutline• Introduction on geothermal systems Introduction on geothermal systems • Geophysical methods Geophysical methods • Seismic Methods Seismic Methods • Larderello – Travale geothermal fields Larderello – Travale geothermal fields • Seismic Data and MethodologySeismic Data and Methodology• Results Results • Conclusions Conclusions • ReferencesReferences• Questions ??Questions ??

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Introduction Introduction

http://geothermal.marin.org

HEAT SOURCE

PERMEABLE FLOW PATH

RECHARGE AREA

CONVECTION FLOW

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http://geothermal.marin.org

5http://geothermal.marin.org

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Geophysical Methods Geophysical Methods

Include : Include : • Thermal surveys : T gradients, T distribution, heat flow Thermal surveys : T gradients, T distribution, heat flow • Resistivity : to delineate field boundariesResistivity : to delineate field boundaries• Gravity : to define intrusive bodies, heat sourceGravity : to define intrusive bodies, heat source• Magnetic survey : boundaries to flows in volcanic Magnetic survey : boundaries to flows in volcanic

areas areas • Magneto-telluric : fracture detection, monitoring, and Magneto-telluric : fracture detection, monitoring, and

regional structure. regional structure. • Seismic methods : passive and active seismicSeismic methods : passive and active seismic

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Seismic MethodsSeismic Methods Passive Methods : Passive Methods : • It can be natural or induced by geothermal activityIt can be natural or induced by geothermal activity• Micro Seismic Survey, can be as MEQ surveyMicro Seismic Survey, can be as MEQ survey• Mainly applied for production monitoring Mainly applied for production monitoring

Active Seismic Active Seismic • Seismic refractionSeismic refraction – only applied in limited extent – only applied in limited extent• Seismic reflectionSeismic reflection – widely applied, with remarkable results – widely applied, with remarkable results Challenges :

• Very costly Very costly • uneasy to manage the data as lower resolution (Vuneasy to manage the data as lower resolution (VP P VVSS change is change is

smaller than in oil), large velocity contrast due to altered rockssmaller than in oil), large velocity contrast due to altered rocks

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Larderello – Travale Geothermal fieldsLarderello – Travale Geothermal fields

• Area of deep field 400km2Area of deep field 400km2• Fluids : tapped within 4000m, Fluids : tapped within 4000m,

4-7MPa, 200 – 350°C 4-7MPa, 200 – 350°C • Shallow reservoir : carbonates, Shallow reservoir : carbonates,

anhydrites, phyllites, quartzitesanhydrites, phyllites, quartzites• Deep reservoir : metamorphic Deep reservoir : metamorphic

series of phyllites, micaschists, series of phyllites, micaschists, gneiss, granitesgneiss, granites

• Cap rock : Flysch and Neogene Cap rock : Flysch and Neogene sedimentssediments

(From Bertani et al., 2005)

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(From Cameli et al, 2000)

Seismic Data Seismic Data

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(From Cameli et al, 2000)

Stacked data – seismic line LAR 36

1 – Fault2 - Flysch/Evaporites formational contact3 – Top of Metamorphic basement4 – Main seismic reflection, deep res. study focus5 – Horizon K

• Decrease in coefficient reflection• Implies well defined geological contact

• Overall poorly defined reflections, but sometimes show high energy character• Probably related to geothermal fluid occurrence• The zone has considerable variation in elastic parameters from boreholes logs data

• Hypothesis : the reflections could correspond to certain fractured rocks within the zone• The study : to examine the hypothesis by :

Theoretical Study

Empirical Study

11(From Cameli et al, 2000)

Migrated data from seismic line LAR 36 with projection of 2 directional wells

1 – Flysch2 - Tectonic Wedges Complex3 – Metamorphic basement4 – Granite5 – Main seismic reflection, deep res 6 – Horizon K Secondary fracture Main fracture

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MethodologyMethodology

Theoretical • Studies the cause and the effect relationship between interesting

petrophysical relationships and seismic response • Techniques : wavelet processing, calibrated acoustic impedance sections,

AVO analysis• Data from 8 wells/boreholes : velocity, density and relevant petrophysical

parameters

Empirical-statistical • Investigates the statistical relationships between reservoir data (injectivity,

productivity) and reflection signals.• Technique : correlation quality between working hypothesis (i.e. fractured

level giving distinctive seismic reflection and real data) evaluated by depth deviation percentage

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(From Cameli et al, 2000)

3710 m

THEORITICAL STUDY

• Large velocity and density reduction at fractured production level (3710m)

• High amplitude of the reflection coefficient and synthetic reflection waveforms

Suggest presence of steam/gas (within the

productive zones)

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• Theoretically, with presence of steam/gas (in productive zones)

• Vp/Vs ratio should cause a decrease • Mod. Reflection coeff. increase or remains constant with increase of incidence ~ AVO increase too

THEORITICAL STUDY - AVO RESPONSE

• As shear velocity data unavailable, the AVO response computed with “what if ” procedure

(From Cameli et al, 2000)

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(From Cameli et al, 2000)

Data for empirical study – VSP within the metamorphic basement

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(From Cameli et al, 2000)

EMPIRICAL-STATISTICAL STUDY

Type of data : ► Fracture data (from prod. Wells)

• Producing zones PF• Scarcely producing zone SPF• No production TLC

► Type of Events

► Deviation depth % < 3% , 3-5 % , 5-10 % , >10%

EventsEvents Detection ofDetection of

Facture Facture Seismic reflectionSeismic reflection

NNNN NoneNone NoneNone

NFNF NoneNone

NRNR NoneNone

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Empirical-Statistical study Empirical-Statistical study

• 73% of seismic reflections correspond to fractured zones, being the depth deviation less than 10%, while the rest (27%) does not correlate or the correlation shows a deviation > 10%.

• The VSP data are much more sensitive compared to seismic surface line data.

• In contrast, this behavior is less evidenced by the TLC fractures.

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Conclusions Conclusions

• The empirical study show that, within the Larderello-Travale deep reservoir, 73% of the seismic reflections are related to permeability with a depth deviation of less than 10%.

• Both theoretical and empirical studies indicate that fractured, steam saturated levels give rise to distinctive and potentially diagnostic seismic features.

• To detect the features noted above, appropriate seismic field acquisition and accurate seismic processing, including wavelet processing and true amplitude and phase control are required.

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• Seismic reflection method has played an important role for identification of deep geothermal targets in Larderrello –Travale fields. It is proven to be the only method providing resolution useful for operative targets deeper than 3 km.

• Importantly, it became clear that the seismic method could provide more than the definition of geological structure, namely, information directly related to geothermal production.

• A reliable correlation has been verified between deep seismic markers and fractured/permeable horizons in the metamorphic basement.

Conclusions Conclusions

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Current status of the FieldCurrent status of the Field

has been producing since 1960s has been producing since 1960s with with 790 MW790 MW capacity from capacity from total total 3232 geothermal power plants, geothermal power plants, providing providing 4,800 GWh/yr4,800 GWh/yr to to 2 million2 million Italian households, Italian households, saving saving 1.1 tonnes1.1 tonnes of oil equivalent of oil equivalent ( about 6.8Mbbl of oil equivalent ) ( about 6.8Mbbl of oil equivalent ) avoiding avoiding 3.8 million tonnes3.8 million tonnes of CO2 emissions of CO2 emissions

(www.europeanenergyforum.eu) (www.europeanenergyforum.eu)

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ReferencesReferences► Primary sources :

o Bertani, R., Bertini, G., Cappetti, G., Fiordelisi, A., Marocco, B.M., 2005, An Update of the Larderello-Travale/Radicondoli Deep Geothermal System, Proceedings World Geothermal Congress 2005, Antalya, Turkey, p. 1-6.

o Cameli, G.M., Ceccarelli, A., Dini,I., and Mazzotti, A., 2000, Contribution of the seismic reflection method to the location of deep fractured levels in the geothermal fields of southern Tuscany (Central Italy), Proceedings World Geothermal Congress 2000 Kyushu - Tohoku, Japan, p. 1025 – 1029.

► Secondary sources :o Keller, G.V., 1981. Exploration for Geothermal Energy. In: Fitch, A.A. (Ed.),

Developments in Geophysical Exploration Methods – 2, Applied Science Publishers., pp. 107-150.

o Manzella, A., Gianelli, G., and Puxeddu, M., 1995, Possible models of the deepest part of the Larderello geothermal field, Proceedings World Geothermal Congress 1995, Kyushu - Tohoku, Japan, p.1279 - 1282.

o Vanorio, T., De Matteis, R., Zollo, A., Batini,F., Fiordelisi, A., and Ciulli, B., 2004, The deep structure of the Larderello-Travale geothermal field from 3D microearthquake traveltime tomography, Geophysical Research Letters, vol. 31, L07613, doi:10.1029/2004GL019432

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Thank you Thank you

and and

Any Questions ???Any Questions ???